As a technique of evaluating a solar radiation amount in a predetermined area using a static satellite image, there has been known a technique disclosed in Patent Document 1. In this technique, a value of albedo and a luminance temperature of an area corresponding to each pixel are obtained from a pixel value of a static satellite image. The obtained results are compared with previously obtained past albedo values and so on in sunny weather at the same time period, whereby fine weather or cloudiness is discriminated. The solar radiation amount is calculated by a predetermined calculation formula according to whether it is sunny or cloudy. The calculation formula uses, for example, a solar zenithal angle, a solar constant, distance between the sun and the earth, various transmittances such as a transmittance associated with ozone absorption, a solar absorptance coefficient of a cloud, and the albedo value. The albedo value is obtained by dividing the reflectance of a pixel by the cosine of the solar zenithal angle.
In the method disclosed in Patent Document 2, utilizing the fact that the amount of reflection and the solar radiation amount are directly associated by a regression coefficient based on a statistical relationship, the solar radiation amount is directly estimated based on the amount of reflection, that is, a pixel value of a static weather satellite image.    Patent Document 1: Japanese Patent Application Laid-Open No. 11-211560    Patent Document 2: Japanese Patent Application Laid-Open No. 2004-118639